*If you can persude your teenagers to continue to wear clothes from supermarkets, not go out, not have a smartphone, eat like a toddler, go to a school that doesn't have a uniform and be happy to spend their time reading library books I'm sure you won't notice an increase in costs.
In the real world teenagers on the whole aren't like that.*
Indeed. If you want your teens to have hobbies, they will cost you. I positively encouraged my teens to pursue things like music lessons (plus the cost of instruments, exam entrance fees, endless ferrying to and from band practice, concerts), Duke of Edinburgh award scheme (again, this costs money and a fair bit of ferrying to meetings), drama groups, martial arts etc etc.
If we couldn't have afforded it, we wouldn't have encouraged it. But we managed to make it affordable and I much preferred them attending extra-curricular activities than stuck in their bedrooms at weekend, or hanging round aimlessly with other bored teens.
School uniform costs are pretty steep too once they are in secondary school.
And just because you don't HAVE to pay for driving lessons, why wouldn't you if you can afford it? Getting your driving licence out of the way when you are 17/18 is really useful .
They both had mobile phones as soon as they started secondary school - which was a fair way from home and we wanted to be in instant contact in the event of missing the bus, bus breaking down, etc etc.
The list goes on. You don't HAVE to buy them anything except food, basic toiletries like shower gel and toothpaste, supermarket clothing. But each family has to decide what's important.
My teens cost a fortune. I don't regret one single penny.